PoF: No achievements for party members in 'Enemy of my Enemy' instances - bug or intentional?

Hey guys,my girlfriend and I have been getting PoF achievements together and stumbled upon this: In the story step 'Enemy of my Enemy', where you need to gather your army of mummies, we went for the Explosives Expert one. She, the instance owner, got it and I didn't. Likewise, in the next step, the Beast chase, we went for the achievement Tag!. I, the instance owner, got it and she didn't. Why is that? Is it a bug or are party members barred for some reason from acquiring the achievements if it's not their instance?

If you are eligible to get it the buff icon for it should appear.

If there is a buff icon and only the instance owner gets it then it is a bug.

If there is no buff icon then it is not.

Actually, this one only counts for the story instance owner. Any other person is transformed into a mummie him/herself. Similar happens in the Tag! achievement. The other persons are some sort of ghost in there that can buff the instance owner and debuff the beast. This is not a bug, it is intended. There are actually a few more of such achievements later on in the PoF story (the end story in example). In this case it has something to do with only instance owner getting some Sword of Sohotin.